1. Field of the Invention
This invention relates in general to traction and hydraulic elevator systems, and more particularly, to distributed control circuits and apparatus located at a car which communicates serially by network signals over a traveling cable with a remote microprocessor elevator controller.
2. Description of the Prior Art
Microprocessors may be pre-programmed to satisfy various safety code requirements in a building configuration. Elevator system safety codes are applicable to both traction and hydraulic car drive apparatus, and this has been given recognition in the fact that advances in the state-of-the-art of solid-state control permits the incorporation of safety circuits into elevator systems with some assurance that component failure does not result in unsafe operation. The likelihood of failure of components used in the present day elevator control apparatus has been minimized by the application of materials testing procedures, statistical use extensions, and appropriate service inspections with periodic and special parts replacements.
There is a historical recognition in accident prevention that many types of failure modes can be prevented. The codification of same and the need to meet the elevator safety code requirements, are exemplified in the mandate that an elevator car is not allowed to travel more than a predetermined distance away from a floor with the car doors open. Previously, this requirement was met by floor level detection apparatus mounted on the elevator car, and it was hardwired through a traveling cable to an elevator controller where the signals were interfaced directly into relay safety circuits. With the introduction of microprocessor based elevator controller, the compliance with the safety codes has gradually shifted to implementation of the codes by programs which can cycle through a safety checking function in a very short time interval. The functions of vast number of relays or arrays of relays found in the historic elevator systems have thus been consolidated into the functioning of microprocessors as controllers which can do a vastly superior job of coordinating all of the multiple demands for elevator service with the control of the car movements very efficiently from floor to floor. This includes car speed transitions for a comfortable ride along with landing and releveling operations at any target floor of the building with door control and safety for the passengers being an overriding and consuming concern.
The current realization of advantages through the use of local area networking for bi-directional serial signal transmission permits an even more efficient distribution of car control circuits for car and door functions local to the car. A remote microprocessor elevator controller communicates with the car control circuits over the traveling cable network which provides the car datalink with the elevator controller being further available for corridor fixture communication operations according to allowed U.S. Pat. No. 4,683,989 entitled "Elevator Communication Controller" which is assigned to the same assignee as is the present application, and it is hereby incorporated by reference into the present application and will be hereinafter referred to as the incorporated U.S. Patent.
The incorporated U.S. Patent describes an addressable communication controller which when addressed by a valid input message, prepares a return message which is automatically clocked out of the communication controller by way of its previously enabled return data interface as the next input message is clocked into the controller, regardless of whether the incoming message is addressed to this communication controller or to another communication controller to control the various elevator car located functions along with the various corridor fixture signal information.
One of the principle problems with an elevator system of the type described above is that compliance to the elevator safety code is done mainly through the microprocessor and the program which is executed thereby. This elevator controller is networked to the car control circuits, but it is remote from the car and its passengers who require a safe passage in any event. A problem arises if there if a failure of the microprocessor or a program failure which is not sufficient to derogate the system operation to its shut-down state with a predictable execution of same. Another problem is present if there is a failure in the bi-directional communication network such as a component failure, an electrical short, or a signal-to-noise ratio outside of the operating requirements.
Yet another problem is present with the releveling of car movement after the landing at a floor, should any of the above failures occur, since the elevator controller may have already signalled the car to relevel with the doors open in order to place the floor of the car level with the corridor floor. This is necessary to compensate for a changing passenger and object weight load with inherent car deflection and drive element cycling to overcome such deflection as caused by either the traction roping stretching-shrinking, in a traction elevator system, or hydraulic pump oil compression-expansion, due to the changing load in a hydraulic elevator system.